This invention relates to siesmic signal sources.
The exploration for underwater petroleum deposits can involve siesmic mapping that is conducted by generating an underwater shock wave or other siesmic signal, and recording the reflections of the accoustic wave. A clean high amplitude pulse which is free of oscillations that can mimic reflections of sound waves, is highly desirable in many situations. One way to produce an underwater pulse is to rapidly expand a rubber enclosure by punping high pressure air therein. However, rapid expansion requires a much larger pressure within the enclosure than in the surrounding water, and such pressure difference can cause bursting of the rubber enclosure and therefore prevent its reuse. Such bursting can be avoided by venting the pressured gas as the enclosure reaches its full expansion configuration. However, such venting is hard to control, and typically results in the enclosure rapidly decreasing in size which results in the generation of bubbles that soon burst and produce subsidiary oscillations. A reusable underwater siesmic signal apparatus which could produce a rapid expansion of the container without rapid decreases in the container size, would be of considerable value in underwater siesmic mapping.